Sheath with extended wings

ABSTRACT

A sheath for a fan airfoil having a leading edge and a trailing edge in a chordwise direction, a tip and a root in a spanwise direction, a suction side and a pressure side includes a solid portion to wrap around the airfoil leading edge; a first wing attached to the suction side of the airfoil; and a second wing attached to the pressure side of the airfoil. At least one of the first wing and the second wing extends at least about 35% of the chord of the airfoil.

BACKGROUND

Titanium alloys and fiber composites are the benchmark classes of materials for fan and compressor blades in commercial jet engines. One reason for the materials being so broadly adopted is that regulations require an engine in service to be capable of ingesting birds while allowing for continued operation or safely and orderly shutdown of that engine. Another reason is that blades must resist cracking from nicks and dents caused by small debris such as sand and rain. Engines with titanium fan blades as well as certain reinforced fiber composite fan blades with adhesively bonded metallic leading edge sheaths are the most common blades used to meet these criteria.

While titanium blades are relatively strong, they are heavy and expensive to manufacture. Composite blades offer sufficient strength and a significant weight savings over titanium, but they are expensive to process. Further, due to their relatively low strain tolerance, composite blades require a greater thickness than otherwise equivalent metal blades to meet bird strike requirements. Greater blade thickness reduces fan efficiency and offsets a portion of weight savings from using composite materials.

Blades made of aluminum or aluminum alloy can result in significant weight savings. However, aluminum alloy blades are softer and lower in strength than titanium or composite blades. Aluminum blades are susceptible to erosion and corrosion, and therefore require coatings. A leading edge sheath made of titanium or nickel can give the aluminum blade added protection without significantly increasing the weight.

SUMMARY

A sheath for a fan airfoil having a leading edge and a trailing edge in a chordwise direction, a tip and a root in a spanwise direction, a suction side and a pressure side includes a solid portion to wrap around the airfoil leading edge; a first wing attached to the suction side of the airfoil; and a second wing attached to the pressure side of the airfoil. At least one of the first wing and the second wing extends at least about 35% of the chord of the airfoil.

A method of fabricating a sheath for an airfoil with a leading edge and a trailing edge in a chordwise direction, a tip and a root in a spanwise direction, a suction side and a pressure side includes forming a solid portion to cover the leading edge of the airfoil; forming a first wing to extend at least about 35% of the suction side of the airfoil in the chordwise direction; and forming a second wing to extend at least about 45% of the pressure side of the airfoil in the chordwise direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a gas turbine engine.

FIG. 2A is a perspective view of a blade with a sheath.

FIG. 2B is a cross-sectional view of the blade with sheath of FIG. 2A.

FIG. 2C is an exploded view of the blade with sheath of FIG. 2A.

DETAILED DESCRIPTION

FIG. 1 is a cross-sectional view of gas turbine engine 10, which includes turbofan 12, fan case 13, compressor section 14, combustion section 16 and turbine section 18. Compressor section 14 includes low-pressure compressor 20 and high-pressure compressor 22. Air is taken in through fan 12 as fan 12 spins in fan case 13. A portion of the inlet air is directed to compressor section 14 where it is compressed by a series of rotating blades and vanes. The compressed air is mixed with fuel, and then ignited in combustor section 16. The combustion exhaust is directed to turbine section 18. Blades and vanes in turbine section 18 extract kinetic energy from the exhaust to turn shaft 24 and provide power output for engine 10.

In one non-limiting example, the gas turbine engine 10 is a high-bypass geared aircraft engine. In a further example, the gas turbine engine 10 bypass ratio is greater than about six (6:1). The geared architecture can include an epicyclic gear train, such as a planetary gear system or other gear system. The example epicyclic gear train has a gear reduction ratio of greater than about 2.3, and in another example is greater than about 2.5:1. The geared turbofan enables operation of the low spool at higher speeds which can increase the operational efficiency of the low pressure compressor 20 and low pressure turbine and render increased pressure in a fewer number of stages.

A pressure ratio associated with the low pressure turbine is pressure measured prior to the inlet of the low pressure turbine as related to the pressure at the outlet of the low pressure turbine prior to an exhaust nozzle of the gas turbine engine 10. In one non-limiting embodiment, the bypass ratio of the gas turbine engine 10 is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor 20, and the low pressure turbine has a pressure ratio that is greater than about five (5:1). It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present disclosure is applicable to other gas turbine engines.

In one embodiment, a significant amount of thrust is provided by the bypass flow path B due to the high bypass ratio. The fan section 12 of the gas turbine engine 10 is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet. This flight condition, with the gas turbine engine 10 at its best fuel consumption, is also known as bucket cruise Thrust Specific Fuel Consumption (TSFC). TSFC is an industry standard parameter of fuel consumption per unit of thrust.

Fan Pressure Ratio is the pressure ratio across a blade of the fan section without the use of a Fan Exit Guide Vane system. The low Fan Pressure Ratio according to one non- limiting embodiment of the example gas turbine engine 10 is less than 1.45. Low Corrected Fan Tip Speed is the actual fan tip speed divided by an industry standard temperature correction of (T /518.7)^(0.5). in which “T” represents the ambient temperature in degrees Rankine. The Low Corrected Fan Tip Speed according to one non-limiting embodiment of the example gas turbine engine 10 is less than about 1150 fps (350 m/s).

The portion of inlet air which is taken in through fan 12 and not directed through compressor section 14 is bypass air. Bypass air is directed through bypass duct 26 by guide vanes 28. Some of the bypass air flows through opening 29 to cool combustor section 16, high pressure compressor 22 and turbine section 18. Fan 12 includes a plurality of blades 30 which spin in fan case 13.

FIG. 2A illustrates blade 30 with sheath 32. FIG. 2B is a cross-sectional view of blade 30 with sheath 32, and FIG. 2C is an exploded view of blade 30 with sheath 32. Blade 30 includes airfoil 34 with leading edge 36 and trailing edge 38 in a chordwise direction, tip 40 and root 42 in a spanwise direction, and suction side 44 and pressure side 46 in a thickness direction. Sheath 32 includes solid portion 48 covering leading edge 36, first wing 50 extending from solid portion 48 over suction side 44 in a chordwise direction and second wing 51 extending from solid portion 48 over pressure side 46 in a chordwise direction. Wings 50, 51 can be tapered. Blade 30 can be made of aluminum (including alloys).

Sheath 32 may be formed as a single piece or may be formed from more than one piece. If formed from more than one piece, pieces of sheath 32 can be secured together (by welding, bonding, etc.) into one piece before bonding sheath 32 onto airfoil 34. This single piece will ensure maximum strength of sheath 32 and therefore maximum protection for airfoil 34. Sheath 32 is generally made of titanium (including alloys) or another material with similar strength to weight ratios and/or other characteristics which would make it ideal to use in protecting airfoil 34 from an impact loading, such as a birdstrike. Alternatively, sheath 32 can be made of stainless steel (including alloys), nickel (including alloys) or other materials.

Sheath 32 covers leading edge 36 of airfoil 34 with solid portion 48 by bonding wings 50, 51 to suction side 44 and pressure side 46 of airfoil 34. Wings 50 can be bonded to suction side 44 and pressure side 46 with various adhesives including, but not limited to, rubber, silicone or epoxy resin. Solid portion 48 of sheath 32 can vary in thickness.

The distance which solid portion 48 of sheath 32 extends out from leading edge 36 (see FIG. 2B) can vary across the span (from root 42 to tip 40) of sheath 32, and can be about 28.70 mm (1.13 inches) in the area of airfoil 34 nearest to tip 40, about 80-100% of the span of airfoil 34. First wing 50 can extend about 35% of airfoil 34 in the chordwise direction at tip 40, covering about 30% of suction side 44 in area nearest tip 40. Second wing 51 can extend about 45% of airfoil 34 in the chordwise direction, covering about 35% of pressure side 46 of airfoil 34 in area nearest tip 40. In the example shown in FIGS. 2A-2C, first wing 50 extends distance D₁, about 88.9 mm (3.5 inches) from leading edge 36 on suction side 44; and second wing 51 extends distance D₂ about 114.3 mm (4.5 inches) from leading edge 36 on pressure side 46. The thickness of each wing 50, 51 can vary depending on solid portion 48 of sheath 32, but can, for example, be about 0.838 mm (0.033 inches). The lengths and percentages for the dimensions of sheath 32 are given for example purposes, and can vary depending on requirements for blade 30, sheath 32 and engine 12. For example, sheath wings 50, 51 could extend over nearly all of the suction and pressure sides 44, 46 of airfoil 34 in some embodiments.

When subject to impact loading, a blade is subject to cracking, delamination (if the blade is a composite laminate blade) and deformation. A blade with a sheath is also subject to delamination of the sheath material from the substructure under impact loading. Lightweight blades, such as aluminum blades are especially subject to deformation during impact loading due to reduced stiffness and strain capability of light-weight materials. Deformation can decrease the aerodynamic performance of a blade, and cracking or delamination can result in catastrophic failure of blade 30.

By ensuring first wing 50 and second wing 51 extend at least about 35% of the airfoil chord or cover a particular amount of area on the suction and/or pressure sides 44, 46, sheath 32 provides extra strength and stiffness to blade 30, allowing blade 30 to be made of lightweight materials, and maintain its original shape and therefore optimal performance and levels of aerodynamic efficiency even under impact loading. Prior art blades often had sheaths that had wings which extended only a few inches onto suction and pressure sides of the blade. This resulted in an inability to perform well under impact loading conditions, such as a bird strike. By extending first wing 50 and second wing 51, sheath 32 is able to better protect airfoil 34. Additionally, wings 50, 51 further provide extra stiffness to airfoil 48 and more surface area for a smooth load transfer during impacts to blade 30. Wings 50, 51 can also be tapered to help to reduce stress discontinuities, therefore reducing the likelihood that wings 50 will peel away from blade 30.

Additionally, when blade 30 is made of aluminum, it must be coated due to aluminum's susceptibility to corrosion. When a coating is needed, blade 30 must be made thinner to account for the coating in aerodynamic performance. A coating is not needed where sheath 32 covers airfoil 34. Thus, as sheath 32 covers a larger area of aluminum blade 30 than past sheaths, the need for coating is reduced and airfoil 34 can maintain a larger thickness, therefor reducing its susceptibility to deformation on impact loading.

A sheath for a fan airfoil having a leading edge and a trailing edge in a chordwise direction, a tip and a root in a spanwise direction, a suction side and a pressure side includes a solid portion to wrap around the airfoil leading edge; a first wing attached to the suction side of the airfoil; and a second wing attached to the pressure side of the airfoil, wherein at least one of the first wing and the second wing extends at least about 35% of the chord of the airfoil.

Additional and/or alternative embodiments include the at least one of the first wing and the second wing extends at least about 35% of the chord of the airfoil in a region of the airfoil near the tip; the first wing extending at least 35% of the chord of the airfoil in a region of the airfoil near the tip; the second wing extending at least about 45% of the chord of the airfoil in a region of the airfoil near the tip; each of the first and second wings extending at least about 35% of the chord of the airfoil in a region of the airfoil near the tip the first wing covering at least about 30% of the suction side of the airfoil; the second wing covering at least about 35% of the pressure side of the airfoil; the sheath being titanium; at least one of the first and the second wings being tapered; and/or the first and the second wings being secured to the sides of the airfoil by bonding.

A fan blade for a gas turbine engine includes an airfoil with a leading edge, a trailing edge, a tip, a suction side and a pressure side; and a sheath with a solid portion that covers the leading edge, a first wing which covers at least about 30% of the suction side of the airfoil and a second wing which covers at least about 35% of the pressure side of the airfoil.

Additional and/or alternative embodiments include the first wing securing the sheath to the airfoil suction side by bonding and the second wing securing the sheath to the airfoil pressure side by bonding; the first wing extending at least about about 35% of the suction side of the blade from leading edge to trailing edge in a region of the airfoil near the tip; the second wing extends at least about 45% of the pressure side of the blade from leading edge to trailing edge in a region of the airfoil near the tip; the sheath being titanium; the airfoil being aluminum; and/or the airfoil being composite.

A method of fabricating a sheath for an airfoil with a leading edge and a trailing edge in a chordwise direction, a tip and a root in a spanwise direction, a suction side and a pressure side includes forming a solid portion to cover the leading edge of the airfoil; forming a first wing to extend at least about 35% of the suction side of the airfoil in the chordwise direction in a region of the airfoil; and forming a second wing to extend at least about 45% of the pressure side of the airfoil in the chordwise direction in a region of the airfoil.

Additional and/or alternative embodiments include the solid portion and the first and second wings are formed by machining and/or said region being near the tip.

While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims. 

1. A sheath for a fan airfoil having a leading edge and a trailing edge in a chordwise direction, a tip and a root in a spanwise direction, a suction side and a pressure side, the sheath comprising: a solid portion to wrap around the airfoil leading edge; a first wing attached to the suction side of the airfoil; and a second wing attached to the pressure side of the airfoil, wherein at least one of the first wing and the second wing extends at least about 35% of the chord of the airfoil.
 2. The sheath of claim 1, wherein the at least one of the first wing and the second wing extends at least about 35% of the chord of the airfoil in a region of the airfoil near the tip.
 3. The sheath of claim 1, wherein the first wing extends at least about 35% of the chord of the airfoil in a region of the airfoil near the tip.
 4. The sheath of claim 1, wherein the second wing extends at least about 45% of the chord of the airfoil in a region of the airfoil near the tip.
 5. The sheath of claim 1, wherein each of the first and second wings extend at least about 35% of the chord of the airfoil in a region of the airfoil near the tip.
 6. The sheath of claim 1, wherein the first wing covers at least about 30% of the suction side of the airfoil.
 7. The sheath of claim 1, wherein the second wing covers at least about 35% of the pressure side of the airfoil.
 8. The sheath of claim 1, wherein the sheath is titanium.
 9. The sheath of claim 1, wherein at least one of the first and the second wings are tapered.
 10. The sheath of claim 1, wherein the first and the second wings are secured to the sides of the airfoil by bonding.
 11. A fan blade for a gas turbine engine, the fan blade comprising: an airfoil with a leading edge, a trailing edge, a tip, a suction side and a pressure side; and a sheath with a solid portion that covers the leading edge, a first wing which covers at least about 30% of the suction side of the airfoil and a second wing which covers at least about 35% of the pressure side of the airfoil.
 12. The fan blade of claim 11, wherein the first wing secures the sheath to the airfoil suction side by bonding and the second wing secures the sheath to the airfoil pressure side by bonding.
 13. The fan blade of claim 11, wherein the first wing extends at least about 35% of the suction side of the blade from leading edge to trailing edge in a region of the airfoil near the tip.
 14. The fan blade of claim 11, wherein the second wing extends at least about 45% of the pressure side of the blade from leading edge to trailing edge in a region of the airfoil near the tip.
 15. The fan blade of claim 11, wherein the sheath is titanium.
 16. The fan blade of claim 11, wherein the airfoil is aluminum.
 17. The fan blade of claim 11, wherein the airfoil is composite.
 18. A method of fabricating a sheath for an airfoil with a leading edge and a trailing edge in a chordwise direction, a tip and a root in a spanwise direction, a suction side and a pressure side, the method comprising: forming a solid portion to cover the leading edge of the airfoil; forming a first wing to extend at least about 35% of the suction side of the airfoil in the chordwise direction in a region of the airfoil; and forming a second wing to extend at least about 45% of the pressure side of the airfoil in the chordwise direction in a region of the airfoil.
 19. The method of claim 18, wherein the solid portion and the first and second wings are formed by machining.
 20. The method of claim 18, wherein said region is near the tip. 